Tissue transglutaminase: a stretch mechanosensor in vascular smooth muscle

The vascular wall is constantly subjected to hemodynamic forces arising from the pulsatile nature of blood pressure and blood flow across different vascular beds. Vascular smooth muscle cells (VSMCs) detect these mechanical cues through specialized mechanosensing molecules and cellular structures, which activate coordinated mechanotransduction pathways to maintain vascular homeostasis. Tissue transglutaminase (TG2) is a multifunctional enzyme that, when localized to the cell membrane, interacts with several known mechanosensitive molecules, including fibronectin, integrins, and G protein-coupled receptors. However, whether TG2 functions as a stretch-activated mechanosensor that integrates and harmonizes mechanotransduction processes in VSMCs remains unknown. We hypothesized that VSMC mechanical stretching activates TG2 to promote F-actin formation and cellular stiffening. We tested our hypothesis in cultured human aortic smooth muscle cells (HAoSMC) that were either left unstretched or exposed to cyclic uniaxial stretching using a Flexcell tension system with 11% elongation at 1 Hz for 6 hours, simulating conduit artery pulsatility. TGM2 knockdown was performed in cultured HAoSMC using siRNA alongside scrambled siRNA as a negative control (n=5-6/condition). To evaluate the effects of TG2 overexpression, cells were transfected with an adenovirus expressing human TGM2 or a control adenovirus (n=6-12/condition). We also tested the role of TG2 activation in isolated mesenteric arteries on their subsequent passive pressure-diameter curves (n=8/condition). All differences reported herein are significant at P ≤ 0.05. Our results show that mechanical stretching increases VSMC TG2 activity (presence of N-epsilon gamma glutamyl Lysine links, 1.3-fold), F-actin content (phalloidin staining, 1.3-fold), and cortical stiffness (assessed via atomic force microscopy, 1.3-fold) relative to unstretched conditions. Notably, the stretching-induced effects on F-actin content and VSMC stiffness were significantly attenuated by either TG2 knockdown or pharmacological inhibition of LIM kinase (LIMK), an enzyme that promotes cofilin deactivation and actin polymerization. We also found that stretching-induced increases in F-actin and VSMC stiffness in TG2 overexpressing HAoSMCs were blunted by LIMK inhibition. Similarly, in isolated pressurized mesenteric arteries, pharmacological activation of TG2 with L-NAME, a nitric oxide synthase inhibitor and TG2 activator, increased vascular stiffness, which was abrogated by LIMK or TG2 inhibition. We further demonstrate that stretch-induced actin polymerization and VSMC stiffening occur via a TG2/RhoA/LIMK/cofilin/actin signaling axis. Collectively, these findings identify TG2 as a stretch mechanosensor whose activity is essential for the adaptive responses of VSMCs to mechanical stimuli. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.